Engine wont run after 6al installation

I have a 6a msd box in my comet drag car .Msd distributor and wires blaster coil .It has been trouble free for almost ten years .I have a new in the box 6al and installed it friday in place of my 6a .My car will not run !It is wired according to the instructions and pretty much like my 6a .I removed the 6al and replaced it with my 6a .It cranks and runs like it always has .I put the 6al back on and it spits sputters backfires pops back through the carb etc.etc. I replace it with the 6a it runs great. Today I took the 6al back to summit and they placed it on the msd tester .It had a spark that would bring the dead back to life .I went home cranked my car with the 6a it ran great .Replaced it with the 6al same old popping spitting wont rev and on and on .I took the 6al back to summit and got a new one .Same story it barely runs .I have a ground cable going from the battery to the block and one to the body .Both boxes are grounded to the engine .I am using the starter solenoid for my hot post the coil wires are hooked up like the instructions say .Is there something I am missing here that isn't in the instruction sheet .I have tried the 6al with and without the tach being connected .I have a new coil no difference .Regardless of anything I have tried if I hook my 6a up it cranks and runs like it always has .The tech at msd said my 6al was bad send it back .Well it works great at summit and my new box acts the same .I plan to install a tran brake and as you all know a 6al box is part of the installation .My wires going to the distributor are hooked up just like the 6a .I cant figure this one out .I was looking for a plug and play .Well this is my second and I am still plugging and tired of playing.Thanks Doug

Do you have the rev limiter plugs in the new box?  If you do, try a diffetent chip.  The one might be  bad.

Is it a digital 6al box?

Double check the "4cylinder/6/8 dial".

Yes this is a digital 6al box .It doesn't have chips there are two dials for the rpms .You don't have a setting for how ever many cyls. you have you have two wires to cut for a six or four cylinder engine .It comes set up for eight cylinders .Thanks to you all for the help .Tomorrow I will call msd but somehow I am not confident in them .

Double/triple check the msd ground. I had a similar issue once and it was from a bad ground connection on the block.

Also try loosening the dist and changing the timimg. The digital box might me doin something to the timing that the standard box wasnt. Ive seen it different ign boxes change the timing ALOT.

Doug, the digital box is real funny about voltage. Also they have a built in start retard

Since you've tried everything...this might sound way off, but run your positive and negative wires (temporarily) directly to the battery. MSDs are picky about their power and ground sources. I had my 6AL box too close to my Vintage Air controller and got weird performance from both. Another time I tried to 'share' a power feed directly to the battery with erratic results. Just an idea.

I looked at the first page of my instruction pamphlet it says .Timing may be affected with the installation of a digital 6al box .Friday when I was trying to crank my comet it was popping back through the carb.Just like retarded timing .Maybe Dirtworker is onto something As far as my wiring goes my 6a box is fine with my connections .I cleaned my head where I have it grounded and the hot wire is hooked in the same spot as my old box .Right at the solenoid where the battery cable is .As far as the timing goes when I call msd and told them everything I have said here their response was get another ignition box from them .They never mention the timing changing .But on the front page of their instruction sheet it says timing may be affected .I hope this is the problem .Somehow my brain cant understand how an ignition box swap could change my timing but with electronics I guess anything is possible .Thanks again fellows tomorrow I will give it another shot hopefully I can move my distributor around with the 6al and all will be good .I am beginning to like my old 6a box .It might be old school but it is simple and reliable

This am after everyone woke up I cranked my comet with the 6a .It cranked and ran fine .I hooked up my 6al and it would barely run like previously .After marking my distributor I advanced it some .My engine sounded much better ,gave it some more timing it will idle now I put my timing light on set it at 18 and all is well .It runs as good as my old box .Dirt worker and Supervel gave me the idea .And on the front page of my instruction sheet it says your timing may change .I was more concerned with the wiring instructions .Live and learn .Thanks everybody for the help Maybe I wont be so boneheaded hooking up the two step and solenoid for the trans brake.Thanks again Doug

I would not recommend an MSD product to anyone. It is not the same MSD. The best box on the market is Daytona-Sensors. This is the engineer that designed the Crane box. Retail is around $595 and you get a digital box with 16MB of data logging capability, coil, and USB cord.